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Weathering and Erosion

2.
Junior Cert Recap
1. What is Weathering?
2. What is Erosion?
3. Describe two types of Weathering
4. What type of weathering is happening in this picture?
5. Where was this picture taken?

3.
Weathering and Erosion
 Weathering refers to the breaking down of rocks into smaller
pieces
 Erosion refers to the breaking down of rocks into their smaller
pieces and the transportation away of the rock fragments,
usually by moving wind, sea currents, rivers or glaciers.

4.
Weathering
 Three types of weathering:
 Mechanical – breaking down of larger rock into smaller
rocks. No chemical change to rock. Example – Freeze thaw
action
 Chemical – a chemical reaction occurs in the rock causing it
to dissolve and forming new substances. Example –
Limestone dissolved by rainwater, forming calcium
carbonate in caves
 Biological – disintegration of rocks due to the actions of
plants/animals

7.
Onion weathering (exfoliation)
 Surface of the rock is peeled away layer by layer – like an
onion
 Caused by heat (causing expansion) and cold (causing
contraction)
 If a rock has different minerals (e.g. Granite, sandstone) can
wear more quickly as different particles expand and contract
at different rates

9.
Salt Crystillisation
 Water drying out leaves salt traces behind (basic process
behind the creation of chemically formed sedimentary rocks)
 If water gets into a crack (like what happens with freeze thaw
action) and evaporates instead of freezing, the salt gets left
behind.
 Over time this salt can build up, putting pressure on the rock,
and the rock can crack
 (Like freeze thaw action, except with salt instead of ice)

11.
Chemical weathering
 Rocks are dissolved (usually by rainwater)
 Rainwater contains chemicals and is slightly acidic from
picking up CO2 from the atmosphere
 Sedimentary rocks are most easily weathered –
cementing agents in the rock are most easily weathered
 The Burren in Co. Clare is a landscape created by
Chemical Weathering.